This invention relates to the field of substrate retention systems. More particularly, this invention relates to electrostatic substrate chucking and dechucking in the course of semiconductor substrate processing.
There are many processes in which the substrate on which semiconductor devices are formed is held in place by gravity alone. In such processes, the substrate is typically held in a horizontal face up position, which tends to be the only orientation available when gravity alone is used to hold the substrate. However, it is often desirable to retain the substrate in an alternate position during processing. In addition, there may be reasons for wanting to retain the substrate in a horizontal position. For example, the process may be one in which the substrate tends to be moved about, such as by the forces of moving fluids. Further, it may be desired to subject the substrate to a process condition that impinges upon the substrate from a very specific angle. Thus, retaining the substrate in a specific orientation during a process such as these improves the process by reducing variability, such as might be introduced by substrates that are in different positions from run to run.
Generally, two different forms of substrate retention are used. In one form, the substrate is mechanically held against a support means, such as a backing plate. Various means, such as clips, springs, or rings, are used to make contact with the front of the substrate and to press against the front of the substrate so as to retain the substrate against the support means. While retaining the substrate using front side contact is a very easily implemented method of retaining the substrate, it unfortunately tends to introduce certain undesirable conditions. There are a variety of reasons for this, most of which relate to the fact that the devices are predominantly formed on the front side of the substrate.
For example, contact with the front side of the substrate tends to increase the likelihood of damage to the devices, such as by physically scratching or otherwise crushing or damaging the devices contacted by the front side contact means. Further, contact on the front side of the substrate during certain steps tends to mask the substrate, in the region of the clips or springs that are used to retain the substrate, from the desired processing that is accomplished while the substrate is retained. For example, the clip that makes contact with the front side of the substrate to hold the substrate against a backing plate tends to partially mask the substrate during a deposition process. By masking the desired processing in various locations on the substrate, the devices to be formed in those locations do not receive the processing that is necessary to function properly. Thus, substrate yield is somewhat reduced and cost is commensurately increased.
For the reasons given above, retaining the substrate by means that contact only the back side of the substrate tend to be preferred in many applications. Unfortunately, there are other issues associated with the back side contact methods used to retain substrates. For example, retaining a substrate by drawing a vacuum against the back side of the substrate is only practical at certain processing pressures. Since a vacuum can only be drawn to a theoretical limit of a pressure of zero, processing which is performed under very low pressure conditions tends to reduce the total amount of force that retains the substrate in place. Thus, as the processing pressure is reduced, there is an increased tendency for substrates to work loose from the retaining means. This, of course, tends to reduce the effectiveness of the substrate retention means.
Another method of retaining substrates using back side contact is an electrostatic chuck. This method works by inducing regional electrostatic charges in the substrate with the electrostatic chuck, and then attracting these regional electrostatic charges with opposing complimentary charges in the electrostatic chuck. The attraction between the opposing complimentary charges in the electrostatic chuck and the induced regional electrostatic charges in the substrate tend to retain the substrate against the electrostatic chuck.
Unfortunately, the substrate may tend to accumulate a residual charge during processing, which residual charge is in addition to the induced regional electrostatic charges. Thus, when the electrostatic chuck is de-energized, the accumulated residual charge in the substrate tends to retain the substrate against the electrostatic chuck to some degree. This condition tends to prevent the substrate removal means from removing the substrate from the electrostatic chuck in a smooth manner, as the substrate may initially stick to and then spring from the electrostatic chuck as the substrate removal means lifts the substrate from the electrostatic chuck and overcomes the attraction between the residual charge in the substrate and the electrostatic chuck.
What is needed, therefore, is a system for reducing the residual charge in a substrate and improving the release of a substrate from an electrostatic chuck.
The above and other needs are met by an improvement to a plasma processing system. A processing chamber contains an environment and processes a substrate. An electrostatic chuck is disposed within the processing chamber, and receives the substrate. The electrostatic chuck also receives grip and release signals, which are operable to enable the electrostatic chuck to selectively grip the substrate and selectively release the substrate.
A radio frequency power supply creates and passes a first radio frequency potential signal to a first conduction path that is connected to the radio frequency power supply. The first conduction path passes the first radio frequency potential signal to a high pass filter that is connected to the first conduction path. The high pass filter inhibits signals lower than a first frequency from passing to the radio frequency power supply through the first conduction path, and passes the first radio frequency potential signal to a second conduction path that is connected to the high pass filter.
The second conduction path receives the first radio frequency potential signal from the high pass filter, and passes the first radio frequency potential signal to a first electrode that is disposed within the processing chamber, and which is connected to the second conduction path. The first electrode receives the first radio frequency potential signal from the second conduction path and emits the first radio frequency potential signal within the processing chamber.
A second electrode is also disposed within the processing chamber. The second electrode receives a second radio frequency potential signal, and emits the second radio frequency potential signal within the processing chamber. The emission of the first radio frequency potential signal and the emission of the second radio frequency potential signal create a plasma from the environment within the processing chamber, and thereby process the substrate. The processing of the substrate tends to create a residual charge in the substrate. The residual charge in the substrate tends to inhibit the selective release of the substrate from the electrostatic chuck.
A direct current power supply, connected to a ground, creates and passes an absolute direct current potential signal to a third conduction path that is connected to the direct current power supply. The third conduction path receives the absolute direct current potential signal and passes it from the direct current power supply to a low pass filter. The low pass filter is connected to the third conduction path, and passes the absolute direct current potential signal to a fourth conduction path that is also connected to the low pass filter. The low pass filter also inhibits signals higher than a second frequency from passing to the direct current power supply through the third conduction path.
The fourth conduction path receives the absolute direct current potential signal from the low pass filter, and passes the absolute direct current potential signal to the first electrode, to which it is connected. The first electrode receives the absolute direct current potential signal from the fourth conduction path, and thereby receives an absolute potential reference.
A controller selectively enables application of the first radio frequency potential signal to the first electrode and application of the second radio frequency potential signal to the second electrode. The controller also selectively enables application of the grip and release signals to the electrostatic chuck. The controller further selectively energizes the direct current power supply to apply the absolute direct current potential signal to the first electrode when reduction of the residual charge in the substrate is desired, and thereby assists in the desired release of the substrate from the electrostatic chuck.
Thus, by applying an absolute potential to the first electrode, the potential of the first electrode is no longer at a relative or floating potential, and a discharge plasma ignited through the first electrode is operable to reduce the charge that tends to accumulate in the substrate. Thus, the alleviation of the accumulated charge reduces the difficulty in dechucking the substrate from the electrostatic chuck. The high pass filter inhibits the absolute direct current potential signal from traveling back to the radio frequency power supply and damaging the radio frequency power supply, and the low pass filter inhibits the first radio frequency potential signal from traveling back to the direct current power supply and damaging the direct current power supply.
In various preferred embodiments of the plasma processing system, the first frequency is between about 100 kilohertz and about 1.4 gigahertz, and the second frequency is between about sixty hertz and about 1.4 gigahertz, and most preferably about sixty hertz. The absolute direct current potential signal preferably has a voltage of between about zero volts and about 500 volts, and most preferably between about zero volts and about 200 volts. Most preferably, the controller is operable to energize the direct current power supply at either a fixed or programmable voltage in an automated fashion upon occurrence of one or more events, or at a programmed point in the processing.
Another embodiment of the invention provides a method for reducing charges accumulated on a substrate, where the substrate resides on an electrostatic chuck in a processing chamber of a plasma processing system. The plasma processing system has a radio frequency power supply connected by a first conduction path to an electrode disposed within the processing chamber. The first conduction path is high pass filtered to inhibit signals lower than a first frequency from passing to the radio frequency power supply from the first electrode. An absolute direct current potential signal is applied to the first electrode through a second conduction path with a direct current power supply. The second conduction path is low pass filtered to inhibit signals higher than a first frequency from passing to the direct current power supply from the first electrode.